1. Field of the Invention
This invention relates to a recording apparatus using ink to effect recording, such as a pen recorder or an ink jet recording apparatus, and to a liquid filter suitable for use with such a recording apparatus.
2. Description of the Prior Art
Generally, in a recording apparatus using ink to effect recording, such as a pen recorder or an ink jet recording apparatus, a filter is provided in the intermediate portion of an ink supply path for supplying ink from an ink container to a recording head. FIG. 1 of the accompanying drawings shows an ink jet recording apparatus according to the prior art. In FIG. 1, reference numeral 1 designates a cylindrical piezo element which may receive and compressively deform an electrical pulse and eject ink droplets 3 from an orifice 2. Reference numeral 4 designates a hard glass tube having the orifice 2 at the tip end thereof and further having the piezo element 1 wound thereon. Reference numeral 5 denotes a lead for transmitting the electrical pulse to the piezo element 1. One end of the lead 5 is connected to the surface electrode of the cylindrical piezo element 1 and the other end of the lead 5 is connected to an inner electrode through plating provided on the end surface of the element. Reference numeral 6 designates a flexible tube connected to an ink container, not shown, and also connected to the open end of the glass tube 4. Reference numeral 7 denotes a liquid filter forced into the tube 6. In the ink jet recording apparatus of the above-described construction, it is desirable that the filter 7 perform the following functions:
1. Block the entry of dust which can clog the nozzle whose opening diameter is several tens of .mu.m;
2. Supply sufficient amount of ink to the nozzle;
3. Prevent bubbles created on the ink container side from entering the nozzle;
4. Prevent rearward escape of the pressure which provides the power when the piezo element 1 is deformed to fly ink droplets; and
5. Absorb any pressure fluctuations created in the nozzle and maintain the meniscus in the orifice in a stable condition when the recording head is mounted on a carriage and is reciprocally moved to right and left.
A particularly important function is preventing the entry of bubbles into the nozzle. If bubbles should enter the pressure chamber, which is a space in the glass tube surrounded by the piezo element, the efficiency of the piezo element 1 will be significantly decreased due to the great compressiveness of the bubbles. Also, if bubbles arrive at the vicinity of the orifice 2, the direction of flight of ink droplets will change or minute droplets will be created and cause unsatisfactory printing and, in the worst case, jetting of ink will become impossible.
Accordingly, preventing the entry of bubbles into the pressure chamber is indispensable for stable operation of the ink jet recording apparatus.
In contrast, the filter 7 heretofore used comprises particles 8 of polyethylene integrally shaped by sintering as shown in FIGS. 2A and 2B of the accompanying drawings, and suffers from various problems.
First, since this filter comprises hardened small particles, some of the particles may fall off when the filter is mounted. This means that the filter for preventing the entry of dust itself becomes a source of particles that can clog the recording head and thus, the manufacturing process used to make the filters must be strictly controlled.
Also, ink 9 tries to fill the spaces between the particles 8 but, an acute-angle portion 10 of 30.degree. or less is unavoidably created between the particles and ink cannot enter such portion. If such an acute-angle portion 10 is present, it means that the filter for preventing the entry of bubbles itself contains bubbles therein. Such bubbles usually cannot be removed even if they are sucked from outside and, as the recording apparatus is used for many years, they are gradually discharged and enter the orifice.